NATURAL PIlILOSOniY. 149 



some trustworthy dry process; and, providing a camera with a 

 couple of rollers, wind off from the supply roller suflieient for a 

 neiratiye. After exposure this would be wound on to the other 

 roller, and a fresh supply at the same moment brought opposite 

 the lens for farther use. The compactness and convenience of 

 such an arrangement will be readily understood. The working 

 out of such an arrangement is a matter of detail which we need 

 not discuss here. 



The exact nature of the material and its mode of preparation 

 are, of course, M. Marion's secret ; but as photographers rarely 

 like to work with materials of the constitution of which they know 

 nothing, we may state at once that there is very little doubt that 

 the basis of this fabric is collodion ; and, although it is named 

 vitrified India-rubber, it is very doubtful whether India-rubber 

 enters at all into its composition. The strong and peculiarly 

 characteristic smell of castor-oil is one of the first characteristics 

 which came under our attention in examining the pellicle. On 

 treating it with benzoline it remains unaltered. It is at once 

 penetrated by ether, and softened, but, like collodion films under 

 such circumstances, not readily dissolved. It burns in the rapid, 

 explosive manner of pyroxyline, leaving a little sticky residue 

 like burnt oil. Dr. Vogel described in our pages about a year and 

 a half ago the "leather collodion" of Herr Grune, made from 

 plain collodion containing 4 per cent, of soluble cotton and 3 per 

 cent, of castor-oil, and this appears to be a substance of a similar 

 constitution. Dr. Vogel proposed to supplement a film of the 

 leather collodion with a layer of India-rubber in certain cases, and 

 he describes the films so prepared as very solid and a little elastic. 

 The object for which the preparation was then proposed was the 

 transfer of negatives. It appears probable that to M. Marion has 

 occurred the happy thought of expanding this idea, and forming 

 a transparent fabric in sheets ready for use, which will have a 

 variety of applications. Whatever the precise nature of material 

 employed, the skill with which it is prepared, and the beautiful, 

 transparent, tough, and flexible pellicle produced, confer a boon 

 on photographers generally. — Photograpliic News. 



PHOTOGRAPHY AT THE FRENCH EXHIBITION. 



In no department of the Exhibition was there more activity of 

 mind displayed than in that allotted to photographs. No recent 

 discovery excites more curiosity and interest, nor calls into play 

 more ingenuity and science and taste, than this of j^rinting by the 

 aid of light. The art, in all its various processes, has become of 

 immense importance,admits of innumerable applications, and gives 

 employment to a host of people, many of them highl}'' endowed. 

 Far more than the discovery of the telescope, of the microscope, 

 or of a perfect balance, it has made a new era in science ; and in 

 the fine arts, also, it has exercised a prodigious influence. Photog- 

 raphy is useful in so many ways, — in astronomy, in ethnology, 

 in anatomy, in botany, in architecture, in land surveying, in engrav- 

 13* 



